Coincidence Events Research Articles

Increased likelihood of compound dry and hot extremes in India

Compound dry and hot extremes (CDHE) are periods of prolonged dry and hot weather. Their joint occurrence typically impacts society and nature stronger compared to the occurrence of the single hazards. Understanding the likelihood, variability and drivers of CDHE is challenging due to the complexity of the climate system involving interactions and feedbacks among atmosphere-land processes. In this study, we first investigate the role of the dependence between precipitation and temperature for the likelihood of CDHEs. We demonstrate that both the dependence strength and its type, i.e. the degree of tail dependence, substantially affect the CDHE likelihood. We then analyze the space-time variation of CDHE characteristics during the Indian Summer Monsoon across India for the period 1961–2014. We find strong negative association and substantial tail dependence between precipitation and temperature in some regions. Event coincidence analysis reveals that low soil moisture preconditioned by dry extremes is responsible for 55–65% of CDHE occurrence. Our analysis of the temporal evolution of CDHE characteristics finds an increasing negative association between precipitation and temperature leading to a 2 to 3-fold rise of CDHE frequency for some regions of India.

The SNR of Positron Emission Data With Gaussian and Non-Gaussian Time-of-Flight Kernels, With Application to Prompt Photon Coincidence.

It is well known that measurement of the time-of-flight (TOF) increases the information provided by coincident events in positron emission tomography (PET). This information increase propagates through the reconstruction and improves the signal-to-noise ratio in the reconstructed images. Takehiro Tomitani has analytically computed the gain in variance in the reconstructed image, provided by a particular TOF resolution, for the center of a uniform disk and for a Gaussian TOF kernel. In this paper we extend this result, by computing the signal-to-noise ratio (SNR) contributed by individual coincidence events for two different tasks. One task is the detection of a hot spot in the center of a uniform cylinder. The second one is the same as that considered by Tomitani, i.e. the reconstruction of the central voxel in the image of a uniform cylinder. In addition, we extend the computation to non-Gaussian TOF kernels. It is found that a modification of the TOF-kernel changes the SNR for both tasks in almost exactly the same way. The proposed method can be used to compare TOF-systems with different and possibly event-dependent TOF-kernels, as encountered when prompt photons, such as Cherenkov photons are present, or when the detector is composed of different scintillators. The method is validated with simple 2D simulations and illustrated by applying it to PET detectors producing optical photons with event-dependent timing characteristics.

New constraints on the dark matter-neutrino and dark matter-photon scattering cross sections from TXS 0506+056

The flux of high energy neutrinos and photons produced in a blazar could get attenuated when they propagate through the dark matter spike around the central black hole and the halo of the host galaxy. Using the observation by IceCube of a few high-energy neutrino events from TXS 0506+056, and their coincident gamma ray events, we obtain new constraints on the dark matter-neutrino and dark matter-photon scattering cross sections. Our constraints are orders of magnitude more stringent than those derived from considering the attenuation through the intergalactic medium and the Milky Way dark matter halo. When the cross-section increases with energy, our constraints are also stronger than those derived from the CMB and large-scale structure.

Activity standardization and half-life measurement of 177Lu

The activity of the 177Lu solution has been measured by means of the CIEMAT/NIST efficiency tracing method. This result has been compared to the previous obtained results received from 4πβ(LS)–γ coincidence and anticoincidence counting. The activities determined with various methods have been found to be consistent.The decay curve of the 177Lu solution has been followed in the TDCR counter to determine the half-life of this isotope. The half-life has been separately determined for double and triple coincidence events. The arithmetic mean value of these two results has been found to be T1/2 = 6.6489(52) d.

Characterising the coincidence of soil moisture – precipitation extremes as a possible precursor to European floods

Studies around the world have shown that increases in extreme precipitation are not directly resulting in reported instances of flooding. Despite the evidence that antecedent soil moisture conditions play a significant role in regulating the runoff response during extreme storm events, fewer works have tried to understand the spatial and temporal dynamics of such coupled interactions. In the present work, we aim to improve our understanding of the dominant spatiotemporal patterns of soil moisture (SM) – precipitation (P) dependence over Europe. Using an event-based, non-parametric Event Coincidence Analysis (ECA) approach, we first quantified the probability of SM preceding P by the precursor coincidence rate. We also examined the statistical precursor relationship between SM-P joint episodes and reported annual flood events using the conditional precursor coincidence rate. The results show that seasonality is a major driving force in the spatiotemporal dynamics of SM-P coupling over Europe. The conditional precursor coincidence rates are in line with previous flood hazard studies over Europe and show the importance of considering such diverse interdependencies in flood risk mitigation. Our work has implications for understanding the occurrence of preconditioned compound events worldwide and provides a vital starting point for characterising the major processes that need to be accounted for in comprehensive state of the art flood risk assessment studies.

Lossy SU(1,1) interferometers in the single-photon-pair regime

The success of quantum technologies is intimately connected to the possibility of using them in real-world applications. This requires the system to be comprehensively modeled including various relevant experimental parameters. To this aim, in this paper, we study the performance of lossy SU(1,1) interferometers in the single-photon pair regime, posing particular attention to the different amount of information contained in the measurement of single counts and of coincidences at the output of the interferometer. To this aim, we derive the classical Fisher information (FI) of both single and coincidence events, and study it as a function of the internal and external losses of the system. Our analysis shows that, in the absence of external losses, the FI of the coincidence events is always higher or equal than the one of single events. On the other hand, in the presence of external losses, the FI of the singles can increase above the one of the coincidences. Moreover, our analysis shows that coincidence measurement can be exploited to partially mitigate the effect of internal losses in the absence of external losses. Finally, comparing SU(1,1) and classical SU(2) interferometers, we find that the former can outperform the classical systems when the internal losses are above 50%.

Nocturnal emergence facilitated by thermally-induced hatching in the Chinese softshell turtle, Pelodiscus sinensis.

The coincidence of hatching and emergence events with favorable conditions is crucial for turtle survival. Nocturnal emergence has been widely documented across marine and freshwater turtles, and has long been suggested as an adaptive behavior that reduces risks of heat stress and predation. To our knowledge, however, studies related to nocturnal emergence have mainly focused on the post-hatching behaviors of turtles, and very few experimental studies have been performed to investigate the effects of hatching time on the distribution of emergence times over the course of a day. Here, we visually monitored the activity of the Chinese softshell turtle (Pelodiscus sinensis)-a shallow-nesting freshwater turtle-from hatching to emergence. Our study provides evidence for the novel finding that (i) the timing of synchronous hatching events in P.sinensis coincides with the time of day when nest temperatures decrease, (ii) the synchrony between hatching and emergence may further facilitate their nocturnal emergence, and (iii) synchronous behaviors of hatchlings in the nest may be effective in reducing the risk of hatchling predation, and predation is more likely to occur in the asynchronous hatching groups. This study suggests that the hatching of shallow-nesting P.sinensis in response to temperature changes in the nest might be an adaptive nocturnal emergence strategy.

Dual-panel polyvinyl toluene scintillator application as a radiation portal monitor device for gamma and neutron detection

Detection techniques for radiation portal monitors (RPMs) are being developed at Canadian Nuclear Laboratories. One of the purposes of RPM systems at the border ports of entry is to detect illegal transportation of special nuclear material (SNM), which can be used for radiation dispersal devices or nuclear weapons production.One of the most widely used detection technologies considered for RPMs is the polyvinyl toluene (PVT) scintillator. PVT is the most widely used material due to its low cost and its capability to be formed into different shapes and sizes. However, the primary limitation of PVT scintillators is their poor energy spectrum resolution, which limits the discrimination between neutron and gamma radiation.In the present work, a method that allows for the discrimination of fast neutron events from gamma events in a PVT-based RPM was investigated. This method uses two sets of plastic scintillators separated by an air gap. The gap increases the travel distances between scattering events to more easily distinguish pulses produced by neutron interactions in the scintillator from those produced by gamma rays. The time-of-flight (TOF) values between the coincident events in these two sets of scintillators were measured. The TOF for neutrons is significantly longer than the TOF for gamma rays. Another distinguishing characteristic of neutrons is that the flight time between these two scintillator panels will vary according to their energy.The results show that TOF measurements can distinguish neutron sources with sufficiently different energies. Therefore, this method is capable of identifying radioactive material based on neutron energy.In addition to the experimental work, Monte Carlo simulations were carried out using MCNP6.2. The simulation showed that the detector setup had an efficiency (which is the ratio of the number of counts recorded by the detector to the number of neutrons that are incident on the detector) of approximately 12%. Also, the MCNP results showed that the thickness of the second panel had a minimal effect on the signal and no effect on the gamma/neutron peak separation, and therefore could be any conveniently available thickness. However, increasing the air gap between panels increased the peak separation distance but reduced the signal, with a gap distance between 50 cm and 100 cm producing acceptable results.

Simultaneous time-skew and time-walk correction for TOF-PET detector

Time-of-flight (TOF) has become a very important technology in PET, as it reduces noise to improve the PET imaging performance significantly. To obtain a high coincidence resolving time (CRT), it is effective to eliminate inter-crystal scattering (ICS). In one-to-one readout detectors, ICS events can be easily eliminated by setting an energy window for each photo sensor. Removal of ICS events improves CRT but greatly reduces sensitivity. In this work, we developed a simultaneous time-skew and time-walk correction method that suppresses the degradation of CRT even when ICS events are used for a whole-body TOF-PET scanner. A TOF detector with one-to-one readout using fast LGSO and multi pixel photo counter (MPPC) was developed to apply the proposed correction method. To maximize the sensitivity, the crystal size was 3.1 × 3.1 × 20 mm 3 and all sides were chemically polished as the surface treatment. The fast LGSO array was optically connected to an 8 × 8 MPPC array so that the crystals and MPPCs were in one-to-one coupling. In the detector calibration, we worked to improve CRT by separating individual crystal clusters into photoelectric absorption and multiple ICSs on a 2D position histogram and performing simultaneous time-skew and time-walk correction. A pair of TOF detectors was assembled and CRT was measured. When ICS events were removed as much as possible, the CRT of 230.4 ps was obtained, but about 80% of the coincidence events were removed as ICS events. On the other hand, with all events including ICS, the CRT was 320.2 ps. Using the proposed correction method, we improved the CRT to 268.5 ps without causing sensitivity loss.

Search for Gamma-Ray and Neutrino Coincidences Using HAWC and ANTARES Data

In the quest for high-energy neutrino sources, the Astrophysical Multimessenger Observatory Network has implemented a new search by combining data from the High Altitude Water Cherenkov (HAWC) Observatory and the Astronomy with a Neutrino Telescope and Abyss environmental RESearch (ANTARES) neutrino telescope. Using the same analysis strategy as in a previous detector combination of HAWC and IceCube data, we perform a search for coincidences in HAWC and ANTARES events that are below the threshold for sending public alerts in each individual detector. Data were collected between 2015 July and 2020 February with a live time of 4.39 yr. Over this time period, three coincident events with an estimated false-alarm rate of <1 coincidence per year were found. This number is consistent with background expectations.

Cosmic muon tomography at the Wylfa reactor site utilising an anti-neutrino detector

An anti-neutrino detector (a prototype of VIDARR) was deployed at the Wylfa Magnox nuclear power station between 2014 and 2016. It was comprised of extruded plastic scintillating bars measuring 4 cm by 1 cm by 152 cm and utilised wavelength shifting fibres (WLS) and Multi-Pixel Photon Counters (MPPCs) to detect and quantify radiation. During deployment, the detector recorded cosmic muon events in accidental coincidence along with the anti-neutrino events. The cosmic muons produced in the upper atmosphere had their paths obscured by the power plant buildings as the cosmic muons originated behind the buildings. Cosmic muons have a significantly higher probability to be attenuated and/or absorbed by denser objects and so one-sided muographic methods were utilised to image the reactor site buildings. In order to achieve clear building outlines a control data set was taken at the University of Liverpool from 2016 to 2018 which had minimal occlusion of the cosmic muon flux by dense objects. By taking the ratio of these two data sets and using GEANT4 simulations it is possible to perform a one-sided cosmic muon tomography analysis. This analysis can be used to discern specific buildings, building heights, and features at the Wylfa reactor site including the reactor core/reactor core shielding using cosmic-ray events equivalent to that which would be seen in ∼ 3 hours of normal operation. This result demonstrates the feasibility of using cosmic muon analysis to determine a segmented detector's location with respect to surrounding buildings, assisted by aerial photography or satellite imagery.

CAGMon: A Novel Tool for Identifying and Diagnosing Coherent Associations and Causalities between Multi-channels of the Gravitational Wave Detector

The ground-based gravitational-wave telescopes such as LIGO, Virgo, and KAGRA are very complicated and sensitive compositions of advanced devices. Therefore, they are influenced not only by the mutual interaction among mechanical and electronics systems but also by the surrounding environment. To categorize and reduce noises from many channels interconnected by such instruments and environment for achieving the detection of gravitational waves, it needs to increase a signal-to-noise ratio and reduce false alarm rate from coincident spurious events. Therefore, it is of great importance to identify associations between inter-correlated channels. In this work, we present a novel tool called CAGMon for identifying (non-) linear couplings between inter-correlated channels, which can be applied to the practical cases of the gravitational-wave detector.

Characterization of two-photon interference between a weak coherent state and a heralded single photon state.

We experimentally investigate two-photon interference between a weak coherent state and a heralded single-photon state, producing from a spontaneous parametric down conversion. Both the unequal spectrum linewidth and average photon number ratio in a given time interval are considered in our model. We obtained excellent agreement between our experimental data and prediction from our model. Furthermore, the range of observing high visibility two-photon interference is significantly extended by isolating coincidence events from two-photon contributions in the weak coherent state. These results may throw some new light on quantum information technology when the two-photon interference with independent sources is required.

Susceptibility of vegetation low-growth to climate extremes on Tibetan Plateau

Both intensity and frequency of climate extreme events have significantly increased over the past decades, which triggered exceptional responses in terrestrial ecosystems. Resolving the responses of vegetation growth to climate extremes are essential but challenging. The Tibetan Plateau (TP), home to fragile alpine ecosystems, is sensitive to increased climatic variabilities and thus an ideal region to characterize various ecosystem response to climate extremes. In this study, we employed event coincidence analysis to detect the susceptibility (quantified by coincidence rate) of vegetation low-growth to four climate extremes (drought, extreme wet, extreme hot and cold) using Normalized Difference Vegetation Index (NDVI) and solar-induced chlorophyll fluorescence (SIF) over TP for the period 2001 to 2018. We found notable changes in the susceptibility of vegetation low-growth to climate extremes along climate gradients, with higher susceptibility to extreme hot generally being found in warmer regions, while higher susceptibility to extreme cold in colder regions. Meanwhile, susceptibility to drought decreased while that to extreme wet increased with increasing precipitation. We also found higher susceptibility of herbaceous plants for drought and extreme hot than woody plants, but their susceptibility to extreme wet and cold was relatively lower. The varied vegetation susceptibility to climate extremes along climate gradient and among different vegetation types were due to the sensitivity of vegetation to climate variability, rather than the intensity or frequency of climate extremes. This study identified the ecological sensitive regions under climate extreme events, and highlighted the risk of decline in vegetation growth under warm-droughts in spite of a wetting climate over Tibetan Plateau.

BINGO: Background reduction techniques for 0ν2β bolometric experiments

BINGO is a project dedicated to explore new methods for background reduction in experiments searching for 0ν2β decay. It is based on bolometers, one of the most promising techniques to search for 0ν2β. CUORE and CUPID-Mo/0 are the main bolometric experiments that have illustrated the most relevant limiting factors on sensitivity the bolometers are facing. Surface αs are the main source of background in CUORE, and this contribution has been mitigated in CUPID-Mo/0 using dual heat-light channels, i.e., a main absorber embedding the 2β decay isotope facing a light detector. In this case, surface α rejection is achieved thanks to the lower α light output compared to β/γ. However, there are still other background components that limit the sensitivity of the experiments, such as pile-ups due to random coincidences of physical events, external γ background and β surface radioactivity. BINGO’s proposed technology aims at reducing the background index down to 10−5 counts/(keV kg yr) in the region of interest, thus boosting the sensitivity on the effective Majorana neutrino mass. This can be achieved by: (i) having a revolutionary detector assembly with a reduction in the passive materials facing the detector; (ii) increasing the light detector sensitivity thanks to Neganov-Luke amplification; (iii) using an active shield, based on BGO scintillators with bolometric light detector readout to surround the experimental volume. The main text describes the listed approaches in detail, as well as the recent results of prototype tests.

Transformation of PET raw data into images for event classification using convolutional neural networks.

In positron emission tomography (PET) studies, convolutional neural networks (CNNs) may be applied directly to the reconstructed distribution of radioactive tracers injected into the patient's body, as a pattern recognition tool. Nonetheless, unprocessed PET coincidence data exist in tabular format. This paper develops the transformation of tabular data into n-dimensional matrices, as a preparation stage for classification based on CNNs. This method explicitly introduces a nonlinear transformation at the feature engineering stage and then uses principal component analysis to create the images. We apply the proposed methodology to the classification of simulated PET coincidence events originating from NEMA IEC and anthropomorphic XCAT phantom. Comparative studies of neural network architectures, including multilayer perceptron and convolutional networks, were conducted. The developed method increased the initial number of features from 6 to 209 and gave the best precision results (79.8) for all tested neural network architectures; it also showed the smallest decrease when changing the test data to another phantom.

Experimental Evaluation of a 3-D CZT Imaging Spectrometer for Potential Use in Compton-Enhanced PET Imaging.

We constructed a prototype positron emission tomography (PET) system and experimentally evaluated large-volume 3-D cadmium zinc telluride (CZT) detectors for potential use in Compton-enhanced PET imaging. The CZT spectrometer offers sub-0.5-mm spatial resolution, an ultrahigh energy resolution (~1% @ 511 keV), and the capability of detecting multiple gamma-ray interactions that simultaneously occurred. The system consists of four CZT detector panels with a detection area of around 4.4 cm × 4.4 cm. The distance between the front surfaces of the two opposite CZT detector panels is ~80 mm. This system allows us to detect coincident annihilation photons and Compton interactions inside the detectors and then, exploit Compton kinematics to predict the first Compton interaction site and reject chance coincidences. We have developed a numerical integration technique to model the near-field Compton response that incorporates Doppler broadening, detector's finite resolutions, and the distance between the first and second interactions. This method was used to effectively reject random and scattered coincidence events. In the preliminary imaging studies, we have used point sources, line sources, a custom-designed resolution phantom, and a commercial image quality (IQ) phantom to demonstrate an imaging resolution of approximately 0.75 mm in PET images, and Compton-based enhancement.

Photofission and photoneutron cross sections for 238U and 232Th

A specific objective of the recent IAEA Coordinated Research Project on Photonuclear Data and Photon Strength Functions (Code F41032; Duration 2016-2019) has been to measure photonuclear cross-section data where needed, for unexplored nuclei and cases of discrepant existing data. A dedicated experimental campaign has been conducted at the laser Compton-scattering γ-ray source of the NewSUBARU synchrotron radiation facility of SPring8, Japan, where photoneutron reactions for 11 nuclei from 9Be to 209Bi have been investigated in the Giant Dipole Resonance energy region. The measurements followed the development of a flat-effi ciency moderated neutron detection array and the associated neutron-multiplicity sorting techniques. The IAEA CRP campaign has been followed at NewSUBARU by new measurements of photofission and photoneutron reactions on 238U and 232Th in the energy range of 5.87 MeV – 20.14 MeV. The neutron-multiplicity sorting of high-multiplicity fission neutron coincidence events has been performed using a dedicated energy dependent, multiple firing statistical treatment. The photoneutron (γ, xn) and photofission (γ, fxn) reactions have been discriminated by considering a Gaussian distribution of prompt-fission-neutrons (PFN) multiplicities predicted by the evaporation theory. We here provide preliminary experimental (γ, n), (γ, 2n) and (γ, F) cross sections, average energies of PFN and of photoneutrons emitted in (γ, n) and (γ, 2n) reactions, as well as the mean number of PFN per fission act. The new 238U cross sections are compared with recent statistical-model calculations performed with the EMPIRE code on existing data.

Review of the Imaging Performance and the Current Status of the Cascade Gamma-Rays Coincidence Imagers

Various studies that have investigated the detection of gamma coincidence events have revealed that design factors and image reconstruction approaches dictate the spatial resolution, coincidence efficiency, and levels of statistical noise of the detection system. In the case of imaging, cascade gamma-ray coincidence (CGC) imagers coupled with collimated detectors offer promising values for both spatial resolution and coincidence efficiency. However, to date, no CGC imager with single or multiple collimated detectors has reported a performance level beyond 6.7 mm spatial resolution (FWHM) and 6.0 ×1ncidence efficiency. Given the recent developments and the current interests in high resolution and localization of an individual decaying nucleus, there is a need for CGC imagers with higher performance in terms of spatial resolution and efficiency. Therefore, deploying a CGC imager coupled with multiple collimated detectors may prove to be of value in nuclear imaging and probably in clinical applications

Isolation-free measurement of single urinary extracellular vesicles by imaging flow cytometry

Urinary extracellular vesicles (uEVs) are promising biomarkers for various diseases. However, many tools measuring uEVs rely on time-consuming uEV isolation methods, which could induce sample bias. This study demonstrates the detection of single uEVs without isolation using imaging flow cytometry (IFCM). Unstained urine samples contained auto-fluorescent (A-F) particles when characterized with IFCM. Centrifugation successfully removed A-F particles from the unprocessed urine. Based on the disappearance of A-F particles, a gate was defined to distinguish uEVs from A-F particles. The final readouts of IFCM were verified as single EVs based on detergent treatment and serial dilutions. When developing this protocol to measure urine samples with abnormally high protein levels, 25 mg/mL dithiothreitol (DTT) showed improved uEV recovery over 200 mg/mL DTT. This study provides an isolation-free protocol using IFCM to quantify and phenotype single uEVs, eliminating the hindrance and influence of A-F particles, protein aggregates, and coincidence events.